code: def __call__(self, data):
      if self._firsttime:
          self.nextstart(data)
          self._firsttime = False
  
      self.next(data)
  
file_path: backtrader/backtrader/flt.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from .metabase import MetaParams
  from .utils.py3 import with_metaclass
label_desc: Use image node_id 2 for calling the Filter obj's underlying member method code with example usage: obj.__call__(data) without return types